The present invention concerns in particular the techniques of wrapper threading in an apparatus for wrapping a roll. In conventional wrapping apparatuses a problem has been how to guide the start end of the wrapper about the roll so as to prevent the wrapper from creasing or detaching from the roll. A creased wrapper or an incorrectly guided wrapper, which is detached from the roll, may cause various disturbances during packaging operations and cause interruptions on the packaging line. A solution to the aforementioned problem has been sought by the application of glue to the inside of the wrapper, at least under the start end of the wrapper. However, the glue debris has been found to adhere to the equipment and cause splashing of the glue and, consequently, soiling of the environment as well as resulting operating disturbances. In addition, possible loose layers on the roll reduce the adherence of the first wrapper layer onto the roll surface.
Glue is not suitable in all cases for adhering the first wrapper layer. For instance, in the packaging of soft and porous paper grades such as different tissue papers or food-compatible papers, the use of an adhesive is excluded, because the adhesive can penetrate several web layers, thus spoiling the outermost layers on the roll. Furthermore, for a variety of reasons, the users of the paper roll may request for a package in which the first layer is not adhered with glue. The use of adhesives, however, improves the guided wrapper threading and the operating reliability of the wrapping station.
Guided threading of the wrapper and wrapping about the roll has been attempted by the use of different kinds of guide belts placed to surround the roll. The number of belts used can be, for example three, of which one is under the roll and one belt is located to both sides of the roll. Such apparatuses are quite expensive and the short belts are unable to conform sufficiently well to the roll surface, in particular, if the roll sizes vary.
U.S. Pat. No. 4,723,395 describes an assembly for wrapping rolls in a wrapper. Such an assembly comprises a support frame surrounding the roll, means for guiding the wrapper about the roll and at least one flexible guide belt which is adapted to compliantly conform to the roll's perimeter and to follow the rotation of the roll. The guide belt is arranged to travel as an endless band shaped approximately as a U-shaped track into which the roll to be wrapped is placed. The inner loop of the track is adapted to pass over four backing rolls which are mounted on a first lever arm and a pair of second lever arms so as to be transferable to rest against the surface of the roll to be wrapped. The belt passing over the backing rolls conforms to the surface of the roll to be wrapped during wrapping at all those points of the perimeter of the roll to be wrapped which remain between the three backing rolls.
A particular problem of such guiding threading with the help of the above described endlessly moving belt is caused by breakage of the belts due to operating disturbances and stress. The belts are stressed, i.e., because the belts must travel at a speed equal to the tangential speed of the roll, whereby the outermost layer of the roll may become creased and detach to form a clump under the belt or between the belts. In dual roll wrapping, the belt can jam between the rolls. The construction of the apparatus is therefore complicated and it conceals the wrapping area of the roll over a large sector of the roll's perimeter, even in the rest position of the apparatus. Because the belt is moved by the rotational motion of the roll, guided by several backing rolls and, moreover, must have a great length, the driving resistance of the belt easily tears the wrapper or the outermost layer of the roll. The transfer lever assembly of the belt becomes extremely complicated, since it must be capable of bringing the constant-length belt to enclose rolls of different sizes.